1. Technical Field
The present invention relates to metering valves, and in particular, to fuel and ignitor valves for use in air and space vehicles.
2. Description of the Related Art
Valves for metering fuel and other combustible media to engines in aircraft and spacecraft are well known in the art, see for example U.S. Pat. Nos. 3,848,806 and 4,561,468. Such valves are used to control the rate at which pressurized fuel is supplied to metering orifices in the combustion chamber through a fuel line. The valves are relied upon to provide consistent and rapid control of flow rates of fuel at various operational stages, such as ignition and during sustained operation as actuated by a servo motor or the like. Their operation is critical to proper performance of the vehicle. Poor valve operation can result in unintended engine shutdown and failure.
These valves often include movable stemmed valve members, or pintles, aligned with the outlet port of the valve for controlling the rate at which fuel flows to an engine. Pintle type valves are typically less affected by the temperatures and pressures of the fuel passing through the fuel chamber of the valve, due to their contoured head and axial movement. However, even pintle valves can be adversely affected by the high pressure conditions of jet engines. High pressure can cause large forces to act on the pintle so as to alter the flow rate of the fuel through the valve.
In one prior art design, the pintle of a metering valve is actuated by a servo motor mounted at right angles to the pintle axis. The servo motor has a pinion gear engaging a rack attached to the pintle, the rack extending along the pintle axis. The rack and pinion ensure that axial forces on the pintle are translated properly to the radial bearings of the servo motor; however, the rack and pinion provides a relatively high gear ratio that may not provide sufficient force on the pintle when used with smaller high speed servo motors. Accordingly, a helical spring is attached to the free end of the rack to provide a countervailing force on the pintle reducing the peak forces that the servo motor must overcome.
A drawback to the use of a spring is that it may only coincidentally balance the force on the pintle at certain valve openings and operating conditions. Further, it adds mass to the actuation mechanism slowing its response speed. The rack and pinion is complex and requires stabilizing guideways.